In May, the federal government simulated an earthquake so massive, it killed 100,000 Midwesterners instantly, and forced more than 7 million people out of their homes.

At the time, National Level Exercise 11 went largely unnoticed; the scenario seemed too far-fetched - states like Illinois and Missouri are in the middle of a tectonic plate, not at the edge of one. A major quake happens there once every several generations.

But Tuesday's earthquake along the East Coast is a reminder that disasters can hit where they're least expected. And if the nightmare scenario comes, government officials worry that state and federal authorities won't be able to handle the "cascading failures" that follow. The results of May's disaster exercise won't be released to the public. But privately, these government officials say they're glad that this earthquake was just a drill - and not the big one. Especially because there are so many nuclear power plants in the fault zone.

National Level Exercise 11, or NLE 11, was, in essence, a replay of a disaster that happened 200 years earlier. On Dec. 16, 1811, a magnitude 7.7 earthquake hit the New Madrid fault line, which lies on the border region of Illinois, Indiana, Missouri, Arkansas, Kentucky, Tennessee and Mississippi. It's by far the largest earthquake ever to strike the United States east of the Rockies. Up to 129,000 square kilometers [50,000 square miles] were hit with "raised or sunken lands, fissures, sinks, sand blows, and large landslides," according to the U.S. Geological Service. "Huge waves on the Mississippi River overwhelmed many boats and washed others high onto the shore. High banks caved and collapsed into the river; sand bars and points of islands gave way; whole islands disappeared." People as far away as New York City were awakened by the shaking.

More quakes, of a similar size, followed. But the loss of life was minimal: Not too many people lived in the area at the time. Today, there are more than 15 million people living in the quake zone. If a similar quake hit, "7.2 million people could be displaced, with 2 million seeking temporary shelter" in the first three days, FEMA Associate Adminsitrator William Carwile told a Congressional panel in 2010 (.pdf). "Direct economic losses for the eight states could total nearly $300 billion, while indirect losses at least twice that amount."

During NLE 11, more than 9,000 National Guardsmen were dispatched to 50 sites around Alabama, Arkansas, Illinois, Indiana, Kentucky, Missouri and Tennessee for mock disaster relief. They were joined by workers from the Food and Drug Administration, state agencies, and charity groups like the American Red Cross. It was a truly massive undertaking - especially considering there were all-too-real tornadoes assaulting the region at the same time.

Still, it was only a fraction of what would be required, if there's an actual catastrophe along the New Madrid fault line. Carwille estimated that 42,000 search and rescue personnel would be required, in the event of a real quake.

Those responders would be severely inhibited in the aid they could provide, noted Stockton, the Pentagon official.

"Electric power would go out, not for days, but for weeks and months in the four state region," he said. "Municipal water systems, they all run on electricity, don't they? Well, people are gonna get thirsty. You need water for firefighting, don't you? Second, all gasoline pumps run on electric power. Same with diesel fuel. So in terms of road mobility, of getting the relief forces in, and evacuating people out - no gasoline? The cascading failures go on and on."

Following the Japan disaster, a task force assembled by the Nuclear Regulatory Commission "recommended sweeping changes to the agency's regulatory approach to safety issues… [and] order utilities to conduct reviews of seismic safety using the latest research, and, potentially, agree to costly upgrades," the Wall Street Journal reported last month. "A major area of concern, federal officials say, is the New Madrid seismic zone."

Will another 1811-style earthquake hit the midwest again? At the Aspen forum, Stockton insisted that "we're overdue." That's overblown, if an independent panel (.pdf) convened by the National Earthquake Prediction Evaluation Council is to be believed. There's a one-in-50 chance of a mega-quake every 50 years. Before 1811, the big ones happened in approximately the years 1450 and 900. Still, this is all a game of percentages. No one can say for sure when the next disaster will strike. And it's worth noting that New Madrid is considered the most active earthquake region east of the Rockies.

Federal officials say the government is in a better position to respond to catastrophes today than it was in the Katrina era; and that FEMA administrator Craig Fugate is a quantum improvement over his predecessor, Michael ("Heckuva Job") Brown. Coordination and communication between agencies, and with aid groups, has skyrocketed.

"We're in terrific shape in the Department of Defense to support FEMA and DHS for what I call normal disasters - the kind of disasters that happen every year or every couple of years," Stockton said.

But despite all the drills, if there's a New Madrid II, any government response will be incomplete.